How ghastly is Gilbert Arenas’ play in general — in particular against the Knicks the other night, filling in for Jameer Nelson? He actually had me feeling sorry for Stan Van Gundy.

Those scanning the boxscore might be fooled into thinking Arenas didn’t play half bad — 10 rebounds, nine points, five assists, five turnovers — but eyewitnesses know better. He was bumbling around like a college rookie redshirt, misfiring eight straight shots — before mercifully downing two in a row late in the fourth quadrant — and committing blunders you don’t read about in the Bible.

Van Gundy could not hide his sheer stupefaction. At the alarming sight of successive second segment fast breaks astoundingly mishandled by Arenas, twice the Magic coach bowed his head in prayer to ask for David Stern’s forgiveness . . . and for the reappearance of Anthony Johnson, Rafer Alston or Penny Hardaway to hold down Nelson while Chris Duhon recovers from a thumb injury.

That’s how far Arenas has tumbled to the bottom of the NBA’s talent chain; the obscenely overpaid ($14.25 million guaranteed for four years), substandard Duhon is considered a step-stool up.

If only Arenas’ stroke was as shot as his confidence. In five previous games to dry-heaving 9-for-11 in New York, he was 8-for-37 and followed that up by going 0-for-2 from deep Wednesday evening in 20 minutes against the victorious Hawks. That makes him 10-for-50 in his last seven.

There ain’t no way to hide those lyin’ eyes. And off what they were subjected to Monday night, I’ve got to believe this may very well be Arenas’ last dance to impress the judges and last chance to contribute something constructive to a championship contender.

I almost feel as sorry for him as I do for stray animals and Van Gundy. The $62M Arenas has coming to him over the next three seasons somewhat subverts that sentiment.

That puckering sound you hear is Magic GM Otis Smith doin’ the Tighten Up, not Archie Bell and the Drells. Based on Smith’s relationship (he was the Warriors’ den mother) with Arenas when he joined the NBA in 2001, he rolled loaded dice with owner Rich DeVos’ millions by assuming that burden — despite Wild Gil’s locker room gun play with Wizards’ teammate Javaris Crittenton, jail time, dependably creepy behavior and a trio of left-knee operations.

September will mark three years since Arenas’ third left-knee operation. Admittedly, the 29-year-old doesn’t vaguely appear to have regained his old quickness or lateral movement.

Van Gundy must’ve insisted Arenas look in the mirror, if not the tape of the Knicks’ game. It suddenly appears to have occurred to him he’s on the verge of blowing a pretty good life, if not a paycheck, though, I assume he remains fairly capable of that, too.

If you’re wondering, the Arenas-Rashard Lewis swap saved Wizards owner Ted Leonsis roughly $30M. Lewis is on the books for two seasons, not three, next year’s $21.1M and $22.7M in 2012-13. However, sources say “just” $13.6M of that is guaranteed.

Leonsis also won’t have to lay out an additional $6.2M, the salary Mike Bibby forfeited next season for the freedom to leave and sign with the Heat.

You’d think Leonsis would be grateful to team president Ernie Grunfeld for the found funds. Think again. When Leonsis bought out the Pollin family and became the Wizards’ majority owner, I’m told he thought about changing leadership but couldn’t find an appealing replacement.

“Everyone likes to hire their own people and Leonsis is no different,” a league source said. “And it’s not as if the team’s record over the last few years or all the bozos Grunfeld brought in favor him staying.” Meaning, look for some of Leonsis’ savings to be used to pay off Grunfeld’s final year and the two remaining years owed coach Flip Saunders.

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One impure Nets’ thought before it becomes outdated:

Deron Williams may be the NBA’s premier playmaker, but he sure missed the point when it counted against the Knicks. His decision-making was atrocious with the score tied at 114.

Three straight times, beginning at the 2:34 mark, as Chauncey Billups and Carmelo Anthony combined for three misses, he put the ball in the hands of a long distance jump shooter — Travis Outlaw in the corner, Anthony Morrow from 3 and his own, beyond the arc — and made no effort to get the ball down low to Brook Lopez.

That was the Nets’ problem when Devin Harris was the caretaker. It should not be the problem now. Williams, who also botched a fast-break opportunity by giving Outlaw a bad pass, isn’t supposed to forget about his big man. Neither is coach Avery Johnson; you might think he’d call Lopez’s play. Then again, you might think Lopez would fight more for position in the low docks but apparently he feels he can shoot from anywhere, so why bother.

At any rate, not until there was one minute left did Lopez touch the ball, Knicks up two, thanks to Melo’s 11-footer. Naturally, he missed the layup.